1. Technical Field
The present invention relates to a driving force control unit for a vehicle which selects one driving force characteristic from a plurality of different driving force characteristics by outside operation (manipulation) and determines driving force based on the selected driving force characteristic.
2. Related Art
According to a so-called electronic control throttle type engine which electrically controls a throttle valve known in the art, an accelerator pedal and the throttle valve are not mechanically linked. Thus, the opening of the throttle valve (throttle opening) can be non-linearly controlled for the operating amount of the accelerator pedal (accelerator opening degree).
For example, a technology disclosed in JP-A-2005-188384 divides the driving condition of the engine into a plurality of driving ranges based on engine rotational speed and accelerator opening degree and creates a map for each of the driving ranges so as to control the opening of the throttle valve in accordance with the operation condition of the engine.
According to the technology disclosed in this reference, excellent driving performance is obtained by increasing potential to the maximum at the time of high-speed running, and driving with reduced power is attained when stopping and running are repeated in such cases as traffic congestion. Thus, excellent drivability can be achieved.
According to the technology shown in the above reference, an appropriate map is automatically selected for each of the driving ranges, and the throttle opening is controlled in accordance with the selected map. In this case, when a vehicle having a high-performance engine such as a turbo engine is running on an ordinary road, the driving range is shifted to a full acceleration range and extremely high acceleration performance is offered by a largest possible amount of operation of the accelerator pedal. Therefore, during running on the ordinary road, it is required that the operation amount of the accelerator pedal is continuously and finely adjusted, which increases nervousness of control over the acceleration.
When power for the engine is excessively reduced, sufficient acceleration is not obtained at the time of high-speed running or running on an upward slope. As a result, the driver feels insufficient power of the vehicle.
In addition, driving force characteristics of the vehicle desired by a driver who prefers economical driving with reduced power are different from those desired by a driver who prefers responsive driving achieving excellent acceleration and deceleration responses. Thus, in case that one vehicle is driven by different drivers having different preferences, it is difficult to provide driving control which satisfies the demands of both the drivers.
Accordingly, it is difficult for one vehicle to satisfy all the demands of the respective drivers, and typically a user selects and purchases a vehicle having a driving characteristic suitable for preference of the user. Since the driving characteristic cannot be changed after purchase, the economical aspect fails when a vehicle having high-power driving characteristic is selected. On the contrary, power is unsatisfactory when a vehicle having highly economical driving force characteristic is selected. It is therefore difficult to obtain both high-power driving characteristic and highly economic driving characteristic from one vehicle, which decreases usability of the vehicle.